The present invention relates generally to methods and materials for the detection of ketones and aldehydes in fluid (liquid or vapor) samples. The invention is particularly directed to the quantitative determination of ketone and aldehyde concentrations in physiological fluids including blood, urine and breath samples. The invention further relates to methods and materials for monitoring the effects of diet, exercise and diabetic conditions through the quantitative measurement of breath acetone levels.
It is known that "ketone bodies" by which term is generally meant acetone, acetoacetic acid and .beta.-hydroxybutyric acid, tend to accumulate in the blood stream during periods of relative or absolute carbohydrate deprivation due to the breakdown of storage triglycerides. The process through which overproduction of ketone bodies occurs is not well defined but is related to increased oxidation of long chain fatty acids by the liver. Specifically, acetoacetic acid and .beta.-hydroxybutyric acid are formed by the liver as intermediates during the oxidation of fatty acid molecules by acetoacetyl coenzyme A. Acetone is formed from the spontaneous decarboxylation of acetoacetic acid. Under normal conditions the intermediate products are further degraded to carbon dioxide and water and the ketone products do not appear at significant concentrations in the bloodstream. Nevertheless, certain metabolic and disease states interfere with the normal degradation of these intermediates which then accumulate in the bloodstream as a result.
The quantitative measurement of serum ketone levels is important because of the relationship between elevated serum ketone body levels and clinical conditions such as diabetes, disorders of the digestive organs, renal insufficiency, uremia and malignant carcinoma. In the course of these disorders, ketone bodies pass into the blood stream and a state of metabolic acidosis (ketosis) occurs. Monitoring for the onset of ketosis is of particular importance in the maintenance of diabetics because the occurrence of ketosis may indicate the need for modification of insulin dosage or other disease management.
The concentration and identity of various ketone and aldehyde components present in the serum may be determined by direct chemical or chromatographic analysis. While such direct analysis provides the most accurate determination of serum ketone and aldehyde concentrations it suffers from numerous deficiencies including the requirement that blood be drawn to provide serum for analysis. Moreover, the analysis must be carried out promptly due to decomposition of acetoacetic acid to acetone during storage. In addition, the analysis of blood serum for ketones and aldehydes by chemical means requires the use of various reagents and procedures which can be complex and inconvenient for consumer use. Further, the use of certain chromatographic techniques such as gas chromatography is often impractical for consumer and many types of professional use.
As a consequence of the limitations of measuring serum ketone and aldehyde levels directly, a large body of art has developed directed to the testing of urine particularly for the presence of ketones. It is known that the concentration of ketones in urine bears an imperfect relationship to serum ketone concentrations. While urine ketone concentrations depend on numerous factors and are not always directly proportional to serum ketone concentrations, testing of urine for ketones is a simple and relatively inexpensive means of monitoring serum ketone concentrations. Such methods are in widespread use by diabetics in both home and clinical settings.
A number of test devices and methods for the determination of urine ketone concentrations are known to the art. Some assays utilize the reaction of acetone with salicylaldehyde in alkaline solution to give the deeply colored orange to red compound salicylalacetone. Any acetoacetic acid in such solutions is converted by the alkali to acetone which further contributes to the color reaction.
Kamlet, U.S. Pat. No. 2,283,262 discloses compositions for the detection of acetone and acetoacetic acid in solutions such as urine. The materials comprise a dry mixture of a member of the group consisting of the alkali metal and alkali-earth metal bisulfite addition products of salicylaldehyde and a member of the group consisting of the alkali metal and alkali-earth metal oxides and hydroxides.
Many assays take advantage of the "Legal" method which utilizes the reaction of a ketone or aldehyde with a nitroprusside (nitroferricyanide) salt in the presence of an amine to form a colored complex. While acetone will react, albeit slowly, with nitroprusside under aqueous conditions, the reaction of acetoacetic acid is some 100 to 200 times faster with the result that "Legal" reactions under aqueous conditions whether detecting "acetone," "acetone bodies" or "ketone bodies" primarily detect acetoacetic acid. The color reaction is believed to occur as a result of a coupling reaction through the nitroso group of the nitroprusside with the ketone or aldehyde to form an intermediate which then complexes with the amine to produce a color characteristic of the specific amine. In forming the complex, the trivalent iron of the nitroprusside is reduced to its divalent state. The color complex, however, is unstable because nitroprusside decomposes rapidly in alkaline solutions. Further, nitroprusside salts are subject to decomposition in the presence of moisture and high pH. Frequently during storage, a brown decomposition product is formed which can interfere with sensitive detection during assays.
While numerous advances and improvements have been made with respect to "Legal" assays for the detection of ketones and aldehydes, such assays are still limited by the instability of nitroprusside at pHs greater than 7. Finally, such assays still measure only the concentrations of ketones in urine and fail to necessarily provide accurate measurements of ketone concentrations in the blood serum.
Of interest to this application is the disclosure of Greenburg, et al., J. Biol. Chem., Vol. 154-155, 177 (1944) which discloses methods for the detection of small amounts of acetone in air and in bodily fluids such as blood and urine. The methods comprise the steps of (1) reacting acetone with 2,4 dinitrophenylhydrazine in a strong acid solution to form the corresponding hydrazone; (2) separating the resulting hydrazone by extraction with carbon tetrachloride and (3) colorimetrically detecting the hydrazone reaction product. Also disclosed by Greenburg, et al., are the properties, that hydrazones, owing to their differential solubilities, may be fractionated with alcohol and that hydrazones give intense colors in solutions of NaOH. Carbon tetrachloride is said to readily extract the yellow colored acetone hydrazone from acid solution while it gives up little upon reextraction with alkali. As a consequence of these solubility characteristics it is said to be possible to eliminate interference from keto acids and to estimate the quantity of acetone hydrazone directly in the carbon tetrachloride. Acetaldehyde 2,4-dinitrophenyl hydrazone is said to be "largely" extracted from carbon tetrachloride by alkali while the concentration of acetaldehyde occurring in the blood causes no interference. Formaldehyde is disclosed to cause no interference because its hydrazone is "completely" extracted by the alkali. The reference further discloses that .beta.-hydroxybutyric acid present in a fluid sample may be converted to acetone by oxidation with acid dichromate. The reference further discloses that acetoacetic acid may be converted to acetone by acid hydrolysis.
Also of interest to the present invention is the disclosure of Leach, et al., Canadian Patent No. 850,155 which discloses a process for the removal of aldehyde and ketone "impurities" from chemical process streams. The process comprises passing a stream containing aldehyde and ketone "impurities" through a bed of a specially treated weak-acid ion exchange resin. The weak acid ion exchange resin is prepared by treatment with hydrazine or substituted hydrazines such as phenylhydrazine, methylhydrazine and 2,4-dinitrophenylhydrazine wherein the weak acid groups are converted to carboxylic acid salts. The invention is said to be particularly suited to the purification of mono-hydroxy alcohols having from 1 to 15 carbon atoms. Aldehydes and ketones which can be removed by the process are said to include formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, butanone-2, acetone and others.
It is well known in the art that breath samples may be assayed for the presence of acetone in order to determine serum acetone levels. Acetone is a relatively volatile compound having a partition coefficient of approximately 330. It readily diffuses from the blood into the alveolar air of the lungs according to an equilibrium relationship. As a consequence of this equilibrium state, concentrations of acetone in alveolar air are directly proportional to those in the blood and measurements of acetone in alveolar air can be used to determine the concentration of acetone in the serum. Crofford, et al., Trans. Amer. Clin. Climatol. Assoc. 88, 128 (1977).
Current methods for the measurement of breath acetone levels include the use of gas chromatography. Rooth, et al., The Lancet, 1102 (1966) discloses the use of a gas chromatograph capable of detecting acetone at concentrations of 2 to 4 nanomole per liter (nm/1) of air with 18 nm/1 being the concentration for breath of normal individuals. Subjects breathe directly into the device and the acetone peak is read after 40 seconds. Reichard, et al., J. Clin. Invest. 63, 619 (1979) discloses gas chromatographic techniques for the determination of breath acetone concentrations wherein breath samples are collected through the use of a calibrated suction flask into which the test subject breathes through a glass inlet tube. These methods and the instruments required for their use are complicated and expensive and tend to be impractical for use by consumers.
Other methods for the measurement of breath acetone levels involve the use of mass spectrographic equipment. Krotosynski, J. Chrom. Sci., 15, 239 (1977) discloses the use of mass spectrographic equipment in evaluating the ketone content of alveolar air. Twelve ketone components of breath were identified with acetone comprising the major component. Mass spectrographic methods suffer from the same limitations, however, as relate to gas chromatographic techniques.
These various colorimetric methods, such as the Legal method, known for detection of acetone in biological fluids are complex, time consuming and necessitate the use of a spectrophotometer of color charts. Moreover, the methods often require the use of high concentrations of alkali or acids. Methods utilizing a ketone reaction with dinitrophenylhydrazine require the use of strong acid solutions making their use unsuitable for use in the home or in a physician's office. In addition, solutions of hydrazine materials tend to be unstable. Alternative methods for the detection of acetone often require the use of complex and expensive apparatus. There thus continues to exist a need for methods for the quantitative determination of fluid acetone concentrations which are simple, accurate, inexpensive and do not require the use of high concentrations of hazardous reagents.
There exists a desire for methods for the measurement of the rate of fat catabolism. It is a particular problem that many individuals undergoing diets are unable to determine their rate of fat-loss because of daily variation in their body fluid content. Significantly, it is known that early in a diet individuals lose high proportions of fluid as compared to fat. Later in their diets, when individuals may still be catabolizing fat at a constant rate they may cease to lose fluids at the previous high rate or may, if only temporarily, regain fluid weight. The experience of hitting a plateau in weight loss or even regaining weight is psychologically damaging and weakens the subject's resolve to continue with the diet often with the effect that the subject discontinues the diet.
Recently, a method has been disclosed for the determination of daily rate of fat loss. Wynn, et al., Lancet, 482 (1985) discloses that daily fat-loss may be calculated by subtracting daily fluid and protein mass changes from daily weight changes. Changes in body water are estimated from the sum of external sodium and potassium balances and protein mass changes are calculated from nitrogen balances. Such a method is complex and time consuming thus making it inconvenient for the consumer.
One set of methods for measuring body fat is by quantitating total body water (TBW). A number of methods are available for determining TBW. These include isotopic dilution procedures using deuturiated water, tritiated water and .sup.18 O-labelled water. Urine, blood serum or saliva samples are collected after a 2 to 4 hour equilibration. The fluid samples are then vacuum sublimed and the concentration of tracer in the sublimate is determined by mass spectrometer, gas chromatography, or infrared or nuclear magnetic resonance spectroscopy. Body composition can also be measured by a bioelectrical impedence method using a body composition analyzer.
Hydrostatic weighing method is a well known method wherein the subject is completely submerged in a tank of water and the body fat is calculated by taking into account the average density of fat and the amount of water displaced. This method is inconvenient and is still not completely accurate because assumptions must be made relating to non-fat density, lung capacity and other factors. Another method for calculating the percentage of body fat utilizes skin calipers to measure the thickness of fat deposited directly beneath the skin. Pincers are used to measure the thickness of folds of skin and fat at various locations on the body. The results of these measurements are compared with standardized tables to arrive at a figure for percentage of body fat. This method, while more convenient than the use of hydrostatic weighing is less accurate. All methods for determination of body fat content suffer from the fact that they do not reveal the rate of fat loss but only the fat content of the body at a particular time. Because means for determining body fat content are of limited accuracy, means for the determination of the rate of fat loss are similarly limited. Nevertheless it is desired that a simple and convenient method be developed for the determination of the rate of fat-loss wherein such a method is capable of distinguishing weight loss due to loss of fat as opposed to weight loss from the elimination of bodily fluids.
Of interest to the present invention are observations that ketosis occurs in non-diabetic individuals undergoing weight loss through diet, fasting or exercise. Freund, Metabolism 14, 985-990 (1965) observes that breath acetone concentration increases on "fasting." It is disclosed that breath acetone concentrations increased gradually from the end of the first day of the fast to approximately 50 hours into the fast at which time the concentration rose sharply in a linear fashion and reached a plateau on the fourth day. The acetone concentration of the plateau was approximately 300 .mu.g/liter (5,000 nM) a hundred-fold increase over the normal value of 3 .mu.g/liter (50 nM). When, instead of fasting, the subject was placed on a "ketogenic" diet with a minimum of 92% of calories derived from fat, the subject suffered a lesser degree of ketosis wherein the plateau had an acetone concentration of approximately 150 .mu.g/liter (2,500 nM).
Rooth, et al., The Lancet, 1102-1105 (1966) discloses studies relating to the breath acetone concentrations of a number of obese and diabetic subjects. When the caloric intake of three non-diabetic obese subjects was reduced, their breath acetone concentrations as measured by a gas chromatograph increased approximately three-fold. On fasting, the subjects' breath acetone concentrations increased to one hundred times normal. Within 16 hours after a heavy meal the subjects' breath acetone concentrations dropped almost to normal. In a study of obese diabetic patients, the authors disclosed evidence that those obese patients who had lost weight in the last three months had higher breath acetone concentrations than those patients who had gained weight.
Walther, et al., Acta Biol. Med. Germ. 22, 117-121 (1969) discloses the results of a study on the effects of continued exercise of a well-trained cyclist. The authors disclose that breath acetone concentration, increases prior to, during and after the cessation of the physical load and reached a maximum 15 to 20 minutes after cessation of the physical load. Breath acetone concentrations approach a normal level one to two hours after the cessation of the physical load. It is suggested that the increased production of acetone is due to the increased utilization of plasma free fatty acids in liver and reduced utilization in peripheral tissue.
More recent studies have shown a correlation between fasting in normal and obese patients and increased blood acetone levels. Rooth, et al., Acta Med Scand. 187, 455-463 (1970); Goschke, et al., Res. Exp. Med. 165, 233-244 (1975); and Reichard et al., J. Clin Invest. 63, 619-626 (1979) all show the development of ketosis in both overweight and normal individuals during fasting. Rooth, et al., (1970) suggests the use of breath ketone measurements as a motivational tool to enforce against dietary cheating. The studies disclose that development of ketosis is slower in overweight than in normal weight individuals. Reichard, et al., discloses that there is a better correlation between breath acetone and plasma ketone concentrations than between urine ketone and plasma ketone concentrations. In addition, Rooth, et al., (1970) discloses that certain urine ketone tests which detect the presence of acetoacetic acid are not entirely reliable because some individuals do not excrete acetoacetic acid in the urine despite increased blood serum concentrations.
Crofford, et al., (1977) discloses the use of breath acetone monitoring for monitoring of diabetic conditions and as a motivational tool in following patients on long-term weight reduction programs. Such monitoring is said to be particularly effective as normalization of the breath acetone is disclosed to occur upon significant dietary indiscretion. Patients' breath samples were monitored using a gas chromatograph and it is suggested that patients be instructed to restrict their caloric input to that which will maintain breath acetone concentrations of approximately 500nM. It is further suggested, though without support, that if breath acetone is controlled at this level and the proper balance of carbohydrate, protein and fat are maintained in the diet that weight loss will occur at a rate of approximately one-half pound per week.